1. Field of the Invention
The present invention relates to an apparatus and a system for performing a reservation of a communication resource.
2. Description of Related Art
In a conventional wireless local area network (LAN), a mobile station could not reserve a resource to an access point of a handover destination in advance before performing a handover from a current access point which a mobile station is currently using to another access point. Here, a resource represents, for example, power used according to a communication rate, a memory capacity, a frequency band, or a communication rate itself. Therefore, when a handover occurs, if an access point of a handover destination cannot secure a resource necessary to maintain a communication, a handover fails.
However, due to the IEEE (The Institute of Electrical and Electronics Engineers) 802.11r standard, even in a wireless LAN, it is possible to reserve a communication resource to an access point in advance before a handover. As a result, the handover fail probability is decreased.
A handover specified in the IEEE 802.11r standard (Draft 7.0) will be described below with reference to FIGS. 1 and 2.
FIG. 1 is a diagram illustrating a configuration of a wireless LAN system. The wireless LAN system of FIG. 1 includes a mobile station 111, a plurality of access points 101 to 107 to which the mobile station 111 have access by a wireless communication, and an authentication server 131 which performs authentication that the mobile station 111 is a mobile station authorized to access a network of a mobility domain, and the access points 101 to 107 and the authentication server 131 are connected via a wire line network.
FIG. 2 is a sequence diagram illustrating a handover sequence specified in the IEEE 802.11r standard (Draft 7.0). It is assumed that the mobile station 111 is under control of the access point 103, is communicating with the access point 103 and is moving toward the access point 104 as shown in FIG. 1. At this time, in order to reserve a resource to the access point 104 in advance, the mobile station 111 first transmits an 802.11 Authentication Request (201). The access point 104 replies an 802.11 Authentication Response to the mobile station 111 (202). After receiving the frame, the mobile station 111 transmits an 802.11 Authentication Confirm frame which contains information such as a request resource capacity such as a mean data rate, a minimum data rate and a peak data rate (203). The access point 104 replies an 802.11 Authentication ACK frame which contains an answer for representing whether to accept a resource reservation or not (204).
If a resource request of the mobile station is accepted, frame exchange for an advance reservation is finished, but if a resource request of the mobile station is not accepted, the mobile station can change a desired resource capacity and then retry to request a resource reservation to the access point 104. Thereafter, if the mobile station issues a Reassociation Request 205 till a Reassociation Deadline indicated in an Authentication ACK frame notified from an access point during a Fast BSS Transition Initial Mobility Domain Association to be performed with an access point existing when the mobile station 111 enters a mobility domain 141 for the first time, a resource reserved through the 802.11 Authentication Confirm frame 203 becomes effective, so that the mobile station 111 can communicate with the access point 104 by using the resource (e.g., see, IEEE 802.11r standard, Draft 7.0, July 2007, Section 11A 6, Pages 61 to 67). The access point 104 transmits a Reassociation Response 206 in response to the Reassociation Request 205.
In Japanese Patent Application Laid-Open (JP-A) No. 2004-266713 (pages 4 to 9), disclosed is a technique that, while performing a handover, a mobile station performs a reservation directly or through another base station to as many base stations as the number of reservation base stations determined based on a priority unique to a mobile station. If a mobile station requests a reservation directly to a base station, a mobile station individually transmits reservation information to as many base stations as the number of base stations. If another base station is used, a mobile station transmits reservation information containing the number of reservation base stations to a base station with which it is communicating, and the base station which has received the reservation information selects as many neighboring base stations as the number of reservation base stations and transmits the reservation information to them. Each base station which has received a reservation request directly from a mobile station or through another base station compares a resource capacity requested by a mobile station to its available resource capacity, and accepts a reservation if an available resource capacity is equal to or more than a request resource capacity and rejects a reservation receipt if an available resource capacity is less than a request resource capacity.